Screw-shaped gear hone and method of forming and using the same

ABSTRACT

A worm-shape or screw-shape hone, for honing gear teeth, has the tooth profile of the basic rack at its normal plane. The hone is formed by molding synthetic polymers in which there are dispersed abrasive particles, to provide a Shore hardness of 15* - 75* and a Young&#39;&#39;s modulus 0.5 - 70 X 103 kg/cm2. The hone is engaged with the gear to be finished and is rotated by a motor with the hone driving the gear. During honing of the gear, the hone is fed parallel to the axis or tooth trace of the gear over the whole face width of the gear. The polymer material may comprise a cocured blend of polyurethane rubber and epoxy resin having a suitable flexibility, good resiliency and high abrasion resistance, and the abrasive particles may comprise Alundum or Carborundum, the abrasive particles being exposed at the working surface of the hone.

United States Patent 091 Ainoura 1 1 Jan. 9', 1973 v[22] Filed:

[56] v ReferencesCited [54] SCREW-SHAPED GEAR HONE AND METHOD OF FORMINGAND USING THE SAME [75] Inventor: Masato Ainoura, Kitashigeyasumachi,Japan [73] Assignees: Tsukihoshi Gomu Kabushiki Kaisha, Kurume-shi;Kabushiki Kaisha Kashiiuji Tekkosho, Kyoto-shi,

Japan Sept. 24, 1970 211' App]. NO; 74,973

[ 30] Foreign Application Priority Data Sept. 30, 1969 Japan ..44/7836l[52] US. Cl ..51/206 P, 51/287 [51] Int Cl ..B24d 5/02, B24b 19/00 58Field Of Sarch.........5l/206 R, 206 P, 394, 395, 51/2s7,29s,299,32s

UNITED STATES PATENTS- 4/1929 Hanson ..5l/287 X Primary ExaminerDonaldG. Kelly Attorney-McGlew and Toren [57] ABSTRACT A worm-shape orscrew-shape bone, for honing gear teeth, has the tooth profile of thebasic rack at its normal plane. The hone is formed by molding syntheticpolymers in which there are dispersed abrasive particles, to provide aShore hardness of 15 75'and a Youngs modulus 0.5 .70Xl0 kg/cm The honeis engaged with the gear to be finished and is rotated by a motor withthe hone driving the gear. During honing of the gear, the hone is fedparallel to the axis or tooth trace of the gear over the whole facewidth of the gear. The polymer material may comprise a co-cured blend ofpolyurethane rubber and epoxy resin having a suitable flexibility, goodresiliency and high abrasion resistance, and the abrasive particles maycomprise Alundum or Carborundurn, the abrasive particles being exposedat the working surface of the hone.

v3 Claims, 15 Drawing Figures PATENTEDJM 9|97a 3.708.925

SHEET 2 OF 5 INKENTOR F G 4 Mosoto Amouro ATTORNEYS PATENTEUJAN 9:975

' SHEET 3 OF 5 F I G. 5 B if PRIOR ART FIG.5A

PRIOR ART INVENTOR Mosoto Ainouro ATTORNEYS 3.708.925 sum 5 BF 5 MaximumPitch Variation INVENTOR- Amoura ATTORNEYS I IN "I 2 Maximum PitchVariation Accumulative Masato Before PATENTEDJAN 9 i975 L Maximam F iG.l2A

FIG.|2B

Maximum Accumulative After Honing 3 Times .blil 9.02m got .iili 80km =251 SCREW-SHAPED GEAR BO E AND METHOD OF FORMING AND USING THE SAMEBACKGROUND OF THE INVENTION In prior gear finishing methods, such as.lapping or gear honing, the gear has been finished with a tool in theform of a helical gear, whose tooth profile is in volute and conjugatewith the desired tooth profile of the gear to be finished.

In lapping, a gear to be finished usually is meshed with a lapping toolof a suitable cast iron, and the gear is rotated by the lapping tooland, at the same time, a compound containing a suitable abrasive forlapping is poured into the meshing parts of the gear and the lappingtool to cut away the slightly projecting parts of the-tooth profile ofthe gear to be finished. However, the life of the lapping tool is short,because a good deal of wear occurs on the tooth surface of the cast ironlapping tool. Furthermore,'it is difficult to obtain the precise toothprofile by this finishing method, as the initial tooth profile of thelapping tool is destroyed by the initial abrasion.

A gear honing method, which is an improvement on a known gear shavingmethod using gear shaving cutters, has been proposed In Japanese Pat.No. 8697/1960. In this method, a rigid honing tool, in the form of ahelical'gear, is used, and the honing tool is formed of plastics orsynthetic resins compounded with abrasive particles to have a hardness,as measured on the Rockwell M scale between 90 points above zero and 40'points below zero. The honing tool is formed precisely to the toothshape conjugate with the desired tooth profile of the gear to befinished, as shown in FIG. 5 A of the drawings. The honing tool isutilized to remove nicks and burrs on the tooth surfaces of the gear tobe finished, and to modify slightly the tooth profile. However, thisgear-shaped honing tool is expensive, as a high degree of technique isnecessary to produce the same in accurate form. Furthermore, the honingprocess is not efficient, asit utilizes only the sliding motion, of therolling'and sliding motions which occur during rotation of the gear tobe finished meshing with the gearshaped hone, and this sliding motion issmall as compared with the peripheral speed of the gear. I

As another method'of finishing a gear, it has been proposed to grind thegear by a grinding wheel in the form of a screw. In this case, the f'screw -shaped rigid grinding wheel is meshed with the gear to befinished, and both are rotated at a precisely correct speed byadditional gearing. Either the grinding wheel or the gear to be finishedis fed parallel to the axis of the gear to be finished, so that the gearteeth are ground by the grind ing wheel. Consequently, the axles of Ithe grinding wheel and of the gear to be'finished must be connected bycomplicated and very precise gearing,'and the grinding wheel has to beformed to a very high precision. The tooth form of the screw-shapedgrinding. wheel must be trued by a large diamond very often, and suchtruing takes a long time. Consequently,the grinding machine is verycomplicated and very expensive. As the grindingwheel should rotate athigh speed, it cannot be used for gears having a pitch larger thanmodule 7 with respect to the dynamic balance of the grinding wheel.

SUMMARY OF THE INVENTION This invention relates to gear honin'gand, moreparticularly, to a novel and improved worm-shape or screw-shape gearhone, a method of forming the gear hone. r

The present invention obviates the above-mentioned disadvantages, and isdirected to a honing tool in the form of a screw and having the toothprofile of the basic rack at its normal plane. The hon'irig tool isformed by compounding synthetic polymers, such as a co-cured blend ofpolyurethane rubber and epoxy resin having a suitable flexibility, goodresiliency and high abrasionresistance. Abrasive particles, such asAlunclum or Carborundum aredispersed in the honing tool, and thecompound is molded so as to expose the abrasive particles on the workingsurface thereof.

' This worm-shape or screw-shape bone is engaged with the gear to befinished and is rotated by a motor, with the gear to be finished beingdriven by the hone. In the invention method of honing a gear,appropriate tooth bearing is obtained on each tooth. surface between thehone and the gear to be finished, and the hone is fed parallel to theaxis or tooth traceof the gear to be finished over the whole face widthof thegear. As a result, the hone cuts away the slightlyprojected partsfrom the correct tooth profile of the gear to be finished, and correctsthe roughness as well as'improves the tooth profile, the pitch accuracy,and the accuracy of the tooth trace, rapidly and easily, to provide adurable and noiseless gear.

An objectof the invention is to super finish, efficiently and simply,the tooth surfaces of hardened gears, hard gears cut after heattreatment, shaved gears and ground gears.

Another objectof the invention is to increase thesurface strength andlife of the gearv A further object of the invention is to produce a gearfor high speed and high load, and whichis noiseless in operation. v v iv I Another object of the invention is to provide such a gear for highspeed and high load noiselessoperation by decreasing thesingle pitcherror, the pitch variation and the cumulative pitch error of the gear. I1

- For an understanding of the principles of the invention, reference ismade to the following description of typical embodiments thereof asillustrated, in the accompanying drawings. I 3 I I BRIEF DESCRIPTION OTHE DRAWINGS 1 t In the drawings: n

FIG. 1 is a front elevation view showing the relative positions andrelative movements of a gear to be finished and a worm-shape orscrew-shape gear finish ing hone; v I I FIG. 2 is a side elevation viewcorresponding to FIG. 1; i

FIG. 3 is a perspective view of apparatus for honing a gear inaccordance with the present invention;

FIG. 4 is a side elevation view, partly in section, illustrating anotherembodiment'of the invention method;

FIGS. 5 A and 5 B are explanatory views illustrating a method of honinggear teeth using a known gear honing tool in the form of a gear;

FIG. 6 is a sectional view illustrating the working relation of theinvention hone to the gear to be finished;

ing the method of producing a worm-shape or screwshape hone inaccordance with the present invention;

FIG. 11 A is an enlarged sectional view showing the tooth profile errorof the tooth surface aftergear cutting and before finishing;

thread of hone 1" and that of the tooth trace'of the gear 2", to befinished, aremade to coincide. Hob saddle 14 is fed upwardly anddownwardly, at a suitable speed, by another independent drivingmechanism, which has not been shown in the drawing. Table need not beangularly displaced, and, in the illustrated arrangement, it is onlynecessary that gear 2 mounted on table 15, can be rotated freely. Hobaxle 13 is rotated in opposite directions in accordance with FIG. 11 Bis an enlarged sectional view' showing the tooth profile error of a gearhoned by the method of the present invention;

FIG. 12 A is a graphic illustration of the maximum cumulative pitcherror, the maximum single pitch error and the maximum pitch variation ofa gear after cutting but before honing; and

FIG. 12 B is a graphic illustration of the same errors of a gear afterhoning by the method of the present invention. i

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring ,to the drawings,FIGS. land 2 illustrate a worm-shape or screw-shape hone l, embodyingthe present invention, as used to. hone a gear 2 to be finished. Asindicated by the arrows, hone 1 is moved parallel'to the axis of gear 2,while being rotated, by a suitable motor, in meshing engagement'withgear 2 to rotate gear 2; 1

FIG. 3 illustrates apparatus for finishing small spur gears and helicalgears in accordance with the present invention. Axle 3 of screw-shape orworm-shape hone 1 is rotated, through aspeed change gear 5, by a motor4. Thegear 2. to be finished is mounted on an arbor 6 rotatablysupported between centers 7a and 7b on a table 8. Arbor 6 vhas a brakedrum 9 s ecured'thereto and cooperablewith brakingmeansincludingabrakeshoe '10 and a'weight l 1. n I Table 8.is angularly adjustable in thedirections in dicated by arrows at to adjust the direction of the screwthread of hone lreliative to the tooth trace of gear 2..

After hone l is engaged with gear 2, hone '1 "is rotated by the. motorto rotate gear '2', with the braking device beingeffective. v v

At the same time, table 8 is fed in the directions indicated by arrows yby another driving gear, which has not been-shown, and thus gear 2' isfed, parallel'to its axis, to the hone 1'. Engagement between thescrewshape or worm-shape hone l'and gear 2' is adjusted by verticalmovement of either the hone axis or the table, to change the centerdistance between the hone axis and the gear axis, and. is adjusted sothat there is some backlash during thehoning operation. Axle 3 of hone Imay be rotated in either directionby motor 4, in accordance withzwhetherthe hone is finishing the right tooth surfaces or the left toothsurfaces of gear 2'.

FIG. 4 illustrates a universal-gear hobbing machine as used to finishalarge diameter gear in accordance with the invention. ,A screw-shape orworm-shape hone 1" is secured to the axle 13 of the hob, and the axle isdriven by an independent motor which has not been whetherthe right of.the left tooth surface of the gear 2" are being finished. Alternatively,both surfaces can be finished simultaneously by firmly inserting thetooth of hone 1", in which the tooth height is lower than that of thegear, between the tooth surfaces of gear 2'? The objectives of thepresent invention cannot be attained unless the material of thescrew-shape or wormshape hone has a sufficient resiliency andflexibility to fit the tooth surfaces of the gear to be finished, doesnot decrease the sharpness, and has a sufficient abrasion resistancewhile not producing clogging .of the grinder. In theprior art, thematerials fora gear hone havebeen selected from hard plastics, such asepoxy resins, amino resins, phenol resins, etc., or the cured and moldedhard plastics just mentioned have been compounded with fibers toincrease the tensile strength. As a hone made from these materials is arigid body having poor flexibility, it' is necessary that it be finishedvvery precisely to a shape having a tooth profile c'onjugate with thedesired finished-profile of they gear to be honed. However, such formingof the hone is very ex pensive.

The characteristics of a hone -for performing the' a blend of 90 20percent of liquid polyurethane shown in the drawing. Hob axle 13isinclined, as in the case of gear hobbing, and the direction of thescrew rubber prepolymer and l0 percent of epoxy resin co-cured withsuitable amines is preferred, but any material can be used providedthat'the physicaliproperties of the-completed hone satisfytheabove-mentioned conditions. I 7 a a v The use of polyurethane rubbersas the principal material for the hone is'for the purpose of improvingthe abrasion resistance of the screw-shapev hone to prevent deformationof the tooth profile, and for improving the accuracy of the finishedgears by the resilient fit of the tooth of the hone to the toothsurfaces, of the gear during the honing operation. However, a honeformed only of polyurethane rubber is too soft to hone sufficiently,especially in the case of quenched gears of high hardness. Consequently,in'accordance with the present invention, the ratio of the epoxy resincompounded with the polyurethane rubber is adjusted in accordance withthe purpose for which the bone is to be used. For example, the ratio ofpolyurethane rubber is increased for finishing gears of soft materials,such as bronze.

The other reasonswhy polyurethane rubber is used as the principalmaterial of the screw-shape or worm shape hone of the invention may bestated as follows:

l. Polyurethane rubber prepolymer, before the curing reaction, isliquid, and can be mixed easily with abrasive particles and with liquidepoxy resin, the latter being supplied for adjusting the hardness of thecomposition. v

2. The mixed composition is convenient for casting into a mold.

3. Polyurethane rubber prepolymer and epoxy resin can be co-cured by asingle curing agent, of the amine or acid anhydride series, andfurthermore the properties of the co-cured blend are good.

4. Polyurethane rubber has a high Youngs module when its deformationspeed is rapid, so as to exhibit the same properties as a rubber ofhigher hardness. Therefore, if the apparatus of the invention isconstructed with a screw-shape or worm-shape hone having a variablespeed of rotation, one hone can act as both a soft and hard hone over awide range, and several kinds of gears, having different hardnessesafter quenching, can be honed under the best conditions by a singlescrewshape hone. This possibility, of changing the hardness of the honeby changing the rotation speed thereof, is a characteristic of thepresent invention which is completely unknown with respect to priorhones of the same type.

These points are emphasized by the examples of compositions for thehone, as set forth in the following table:

REOEIP ES 6 uniform products. Referring to'FlG. 9, abrasive particlesare placed in the cavity 19 of a mold comprising a base 16,.an outermold part 17 and a center mold part 18, and the upper surface of theparticle layer is leveled. A reservoir 20 communicates with the bottomof cavity 19 and is filled with the liquid polymer composition. Theliquid surface is gradually leveled up from the under part of theparticles to the upper surface of theparticle layer, and the mass isheated, with the mold, to set the polymer blend.

With some conditions of particle size or shape of the abrasiveparticles, viscosity of polymer blends, etc., a procedure as shown inFIG. 10 is adopted. Abrasive particles are completely mixed with theliquid polymer blend, casted into the cavity 19 of a mold, the cover 21is set, and the blend is heated to cure, with the mold being rotated byasuitable means for preventing sedimentation of the abrasive particles.

When the ratio of the polyurethane rubber used is too great and adhesionbetween the abrasive'particles and the polymer blend is insufficient,the surface of the abrasive particles are previously coated with epoxyresin, verythinly, to improve the adhesion.

Honing tests with 10 species of screw-shape or worm-shape hones, moldedas above mentioned, were made withthe apparatus shown in FIG. 3, and theresults are shown in the last line of the preceding table.

FOR AND PROPERTIES OF BONES Test number 1 2 3 4 5 6 7 8 9 10 Receipe: IY

Polyether-polyurethane prepolymer. 100 90 6O 50 25 0 90 60 50 25 Epoxyresm.... 0 10 40 50 75 100 10 40 50 72 Curing agent of amine serie 1113. 8 22. 2 26 32 45 13. 8 22. 2 25 32 Plastieizer 0 0 0 0 0 10 0 0 0 0Abrasive grains WA #320. 214 218 226 228 234 248 0 0 0 0 Abrasive grainsWA #120. 0 0 0 0 0 0 269 278 282' 289 Volume percent of abrasive grains35 35 35 35 35 35 40 40 40 Properties after curing:

Tensile strength (kgJcmfl) 215 1 186 395 561 676 860 149 307 ,433 520Elongation rcent) 120 90 12. 5 2. 5 -0 25 7. 5 2. 5 Shore D har ess 2226. 6 36. 0 42. 5 60. 0 82. 5 24. 0 34. 0 39. 0 46. 5 Young's modulus(1t) kgJcmJ) 0. 32 0. 65 4. 65 30. 4 b8. 9 76.7 1. 03 7. 74 73. 8 63Yielding point (kgJcmfi) v 1, 150 1, 270 1, 615 1, 920 780 869 1, 500Impact strength (IZOD kg.-cm./cm. 30 v 30 6. 22 4. 53 2. 28 1. 31 30 4.72 2. 99 2. 36 Result of betting test I Bad Good Good Good Good Bad GoodGood Good Good State 01 finished surface In the foregoing table, thecarifigige'fit is :47"; The detailsof one example are as follows: i

methylene bis-(2-chloroaniline), the plasticizer is dioctyl phthalate,and the epoxy resin is Epikote 828,'which is a liquid epoxy resinproduced by Shell Oil Company and a condensate of epichlorohydrine andbisphenol A. The abrasive particles are white Alu'ndum, and theassociated numbers indicate the mesh sizeof the particles.

The compositions mentioned in the table are prepared and molded andcured with heat top'rovide screw-shape or worm-shape hones. When theabrasive particles are added into the liquid polymer blends and the moldis filled, if the liquid polymer blends are in too small amount ascompared to the abrasive particles, the molded products have voids inthe interior and reduced strength. On the other hand, if the liquidpolymer blends are too great in quantity, as compared to the abrasiveparticles, the abrasive particles form sedimentation to producenon-uniform products. Consequently, in the present invention, specialprocedures,

as shown in FIGS. 9 and 10, are adopted to produce item of the testedscrew-shaped hone normal module 1 pitch circle diameter outer'diamcteri072 mm axial pitch 9.43 mm pressure angle 20 lead angle 143 right-handsingle I thread worm kind of screw *SNCM 9 is unickel-chromium-molyhdenum steel in accordance will Japanese industrialStandards of I965, and the chemical composition is as follows: 7

c 0.44 -0.5%, Si 0.15 0.35%,-Mn 0.60 0.90%. P less than 0.030%, 3 lessthan 0.030%, Ni 1.60 2.00%; Cr 0. 60 1.00%, Mo 0. l 5 0.30%.

in tests under the above-mentioned conditions, the

honing required only about 40 seconds for the tooth surface of the gearto be finished to have a mirror-like finish.

Thepitch errors of the gear are measured and shown in FIGS. 12A and 128,with FlG. 12A illustrating the pitch errors before honing and FIG. 12Billustrating the pitch errors after honing. The pitch errors become verysmall after honing, and also the roughness of the tooth surface isgreatly minimized. The values are as follows:

Before After honing honing (micron) (micron) Tooth profile error 13 4Tooth trace error 6 3 Maximum accumulative pitch error 35 7 Maximumsingle pitch error 24 10 Maximum pitch variation 35 7 The honing resultswith the screw-shape or wormshape hones produced by the 10 compositionsshown in Table l have beentested. With the'hone having composition (6),i. 'e., epoxy resin only, the gear is finished to have a very niceappearance, but is cut a good deal near the pitch points, with theaddendum and the dedendum being cut a slight amount.

With a hone formed from composition (1), Le, from polyurethanerubberonly, the gear is not readily cut but is only glazed, as by buffing, andno effect can be attained even by changing the ratio of abrasiveparticles or by increasing the angular velocity of the screwshape orworm-shape hone. With hones having any of the other 8 compositionssuggested in the table, satisfactory results are obtained. I

The method of the present invention can be compared with a prior arthoning method using a helical gear, by reference to FIGS. 5A and SBiFIG. 5B shows howhone 22, in the form of a helical gear, is engagedcutting by abrasive particles with the screw-shape or worm -shape honeof the present invention is completely different from that of honingusing a helical gear type hone.

The engagement between a helical gear type bone and the gear to befinished is composedof rolling contact, and sliding contact, and thespeed-and magnitude of the slide are small as compared to the peripheralspeed. On the contrary, the contact between a-screwshape hone and thegear to be finished is solely a Sliding contact, with the peripheralspeed of the screw-shape hone being the same as the sliding speed.Furthermore, the sliding speed and magnitude are greater by far than inthe prior method, and thus the cutting efficiency is very high and thefreedom of electing the working con ditions is increased. Also, themeans for mounting the gear to. be finished is simple, as the rotationspeed of the gear is small compared with that of apparatus used in priorart methods.

Additionally, as at least two .or three turns of the thread of thescrew-shape hone alwayscontact with an equal number of teeth'of the gearto be finished, the

contacting pressure is concentrated only on the projections of the toothsurface, and the cutting quantity'is greatest'at these parts, therebyincreasing the pitch accuracy a great deal.

Another characteristic of the present invention is that the area oftooth contact surface of .the screwshape bone is as shown in FIG.v 6,and the number of I working-abrasive particles is high near the pitchpoint e prior artpractice, and FIG. 5A is an external view. At

the engaged pitch point' P, the surface velocity of gear 23 in atangential direction'is v and that of the hone is v Therefore, a slideof v;, is caused between the engag ed tooth surfacesfThe sum of thisslide and themvolute' slide, which is zero at the engaged pitch point Pand which is larger at the addendum and ,the dedendum, is the base forthe abrasive particles ofv the hone to cut the tooth'surface. Howeventhespeed and magnitude of this slide is-small as compared with theperipheral speed of the gear.

FIG; 6 illustrates an example ofvthe cutting vaction caused by contactof the tooth surface of a screw-shape hone after it is engaged with thegear to be finished, and with the two elements being engaged in theorder of a, b, c, d, e. FIG. 7 illustrates the honed surfaces resultingfrom contact of: the tooth surface of the gear to be finished, at eachmoment, at the positions a, b, c, d, e;

The screw-shape or worm-shape hone of the invention bends elastically,and the area of metal removal by contact becomes greater by increasingthe contact pressure. At each moment during the engagement, the abrasiveparticles in the hone slide in the directions of the arrows shown in dotand dash line with respect to each of the honed areas. Thus, themechanism of and small at the addendum a and the dedendum e. Also, thecontact pressure is high at' the, points, so that the addendum anddedendumarehoned'substantially, asshown in FIG. 8; Thus,-crowning can bemodified along the tooth profile by establishingsuitable workingconditions. The screw-shape hone of the present invention is alsoelastic, and the dedendum is more rigid than the addendum. Therefore,the addendum of the gear tends to-be cut more than does the dedendumthereof.

' Especially, as in quenched gears the tooth surface at the addendumtends to swell due tothe strain from quenching, this tendency of cuttingthe addendum more'than the dedendum is very effective.

Another characteristic of the present invention is that the gear can befinishedwith the screw-shape hone by changing the center distance of thehoneand the gear a'very small amount at a suitable time. As an exampleofthe method, thescrew-s'hape hone is constructed with a double eccentricaxle which can rotate and revolve at the same time, and the center ofthe amounts periodically with rotation of the hone, using a cammechanism. By so doing, the abrasive particles work even moreefficiently, the tendency of clogging or vitrification is obviated, andthe honing is efficiently effected. These procedures could not be usedin the prior art gear finishing methods, and the present invention isespecially efficient when it is intended to scrape off the.

. high points and irregularities on theteeth of the gear to be finished,especially the high points of undulations at high speed.

9 As compared with helical gear honing, of the prior art, in the presentinvention the elastic screw-shape or worm-shape hone can be producedeasily and cheaply, and has a high honing efficiency. The gear can befinished in a very short time and using very simple apparatus, todiminish the roughness of the tooth surface,

being rotated to serve as the only driving means for a rotatable gearhaving the teeth to be honed, said hone having a worm profilecorresponding to the gear teeth profile, and comprising abrasiveparticles dispersed in a molded resilient polymer material having aShore hardness ofl5 and a Youngs' modulus of 0.5 70 l0 kg/cm 2. Aworm-shape hone, as claimed in claim 1 in which said polymer material isa cured compound of polyurethane rubber and epoxy resin. I

3. A worm-shape hone, as claimed in claim 1, in which said polymermaterial is a cured compound of 90 20 percent of polyurethane rubber and10 percent epoxy resin.

2. A worm-shape hone, as claimed in claim 1, in which said polymermaterial is a cured compound of polyurethane rubber and epoxy resin. 3.A worm-shape hone, as claimed in claim 1, in which said polymer materialis a cured Compound of 90 - 20 percent of polyurethane rubber and 10 -80 percent epoxy resin.